1. Field of the Invention
The present invention relates to an adjustable asymmetric available saturation flux transformer, more particularly, to a linear compensation transformer adapted for a horizontal deflection circuit of a cathode-ray tube (CRT), said transformer having a function for modifying left-side lengthened distortion of an image by compensating a deflection current of the deflection circuit. Various compensation conditions can be satisfied by adjusting a magnitude of current applied to the transformer so as to be adapted for various horizontal scan frequencies. Utilizing the transformer in accordance with the present invention, a problem of magnetic-field interference due to a conventional linear compensation transformer can be avoided.
2. Description of Related Art
In a current design for a horizontal deflection circuit of a CRT, a horizontal scan line scans a screen from a left-side to a right-side thereof. Since a deflection current of the deflection circuit has a continuous sawtooth waveform, impedance corresponding to a scan duration occurs exponential distortion, resulting in lengthening of a left-side of an image displayed on a screen. Such distortion can be expressed by an expression as follows: EQU d(%)=(1/2)ts(Ry+rs)/Ly!.times.100%
wherein
Ly: inductance of a deflection coil of the deflection circuit PA1 ts: scan duration PA1 Ry: impedance of the deflection coil PA1 rs: inner impedance of a transistor of the deflection circuit
For example, referring to FIG. 3, a circular image 41 in a display region 40 of the screen of the CRT is deformed at the left-side thereof, that is, a lengthened region 42 is generated at the left-side of the image 41. Therefore, the resulting image cannot be exactly circular.
To solve this problem, a conventional method provides a horizontal deflection circuit for a multi-frequency display or CRT, as shown in FIG. 2B. A multi-frequency selecting switch SW automatically switches to select a proper one of a set of anti-saturation coils 60 having different inductive impedances, the selected anti-saturation coil 60 cooperates with the deflection coil 50 of the horizontal deflection circuit to achieve compensation of image horizontal distortion for a certain horizontal scan frequency.
When positive and negative currents flow through the respective anti-saturation coils 60, the coils 60 present different degrees of saturation. To modify the distortion, a proper one of the anti-saturation coils 60 is made to be in a non-saturated state, so as to adjust the magnitude of current passing through the deflection coil 50.
However, utilizing the above construction to perform linear compensation for horizontal deflection requires a quantity of anti-saturation coils 60 to proceed with the compensation of horizontal distortion for various frequencies. Therefore, the construction may be too complicated.
Each of the anti-saturation coils 60 is structured as shown in FIG. 2A. The anti-saturation coil 60 comprises a core 62, a linear compensation coil 61 wound on the core 62, and a permanent magnet 63 combined to an end of the core 62. Such a structure is a "open magnetic loop", that is, there is a problem of magnetic-field interference during operation thereof. The phenomenon of magnetic-field interference intends to influence the CRT, resulting in degradation of color purity and color convergence.
In addition, as the horizontal scan frequency of a display is being increased, the necessary quantity of anti-saturation coils is increased proportionally. Accordingly the problem of magnetic-field interference becomes even more serious, and the manufacturing cost is also increased.